# The MIT License (MIT) # # Copyright (c) 2017 Tony DiCola for Adafruit Industries # # Permission is hereby granted, free of charge, to any person obtaining a copy # of this software and associated documentation files (the "Software"), to deal # in the Software without restriction, including without limitation the rights # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell # copies of the Software, and to permit persons to whom the Software is # furnished to do so, subject to the following conditions: # # The above copyright notice and this permission notice shall be included in # all copies or substantial portions of the Software. # # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN # THE SOFTWARE. """ `adafruit_max31865` ==================================================== CircuitPython module for the MAX31865 platinum RTD temperature sensor. See examples/simpletest.py for an example of the usage. * Author(s): Tony DiCola """ import math import time import adafruit_bus_device.spi_device as spi_device # Register and other constant values: _MAX31865_CONFIG_REG = const(0x00) _MAX31865_CONFIG_BIAS = const(0x80) _MAX31865_CONFIG_MODEAUTO = const(0x40) _MAX31865_CONFIG_MODEOFF = const(0x00) _MAX31865_CONFIG_1SHOT = const(0x20) _MAX31865_CONFIG_3WIRE = const(0x10) _MAX31865_CONFIG_24WIRE = const(0x00) _MAX31865_CONFIG_FAULTSTAT = const(0x02) _MAX31865_CONFIG_FILT50HZ = const(0x01) _MAX31865_CONFIG_FILT60HZ = const(0x00) _MAX31865_RTDMSB_REG = const(0x01) _MAX31865_RTDLSB_REG = const(0x02) _MAX31865_HFAULTMSB_REG = const(0x03) _MAX31865_HFAULTLSB_REG = const(0x04) _MAX31865_LFAULTMSB_REG = const(0x05) _MAX31865_LFAULTLSB_REG = const(0x06) _MAX31865_FAULTSTAT_REG = const(0x07) _MAX31865_FAULT_HIGHTHRESH = const(0x80) _MAX31865_FAULT_LOWTHRESH = const(0x40) _MAX31865_FAULT_REFINLOW = const(0x20) _MAX31865_FAULT_REFINHIGH = const(0x10) _MAX31865_FAULT_RTDINLOW = const(0x08) _MAX31865_FAULT_OVUV = const(0x04) _RTD_A = 3.9083e-3 _RTD_B = -5.775e-7 class MAX31865: # Class-level buffer for reading and writing data with the sensor. # This reduces memory allocations but means the code is not re-entrant or # thread safe! _BUFFER = bytearray(3) def __init__(self, spi, cs, rtd_nominal=100, ref_resistor=430.0, wires=2): self.rtd_nominal = rtd_nominal self.red_resistor = ref_resistor self._device = spi_device.SPIDevice(spi, cs) # Set wire config register based on the number of wires specified. if wires not in _WIRE_MAP: raise ValueError('Wires must be a value of 2, 3, or 4!') t = self._read_u8(_MAX31865_CONFIG_REG) if wires == 3: t |= _MAX31865_CONFIG_3WIRE else: # 2 or 4 wire t &= ~_MAX31865_CONFIG_3WIRE self._write_u8(_MAX31865_CONFIG_REG, t) # Default to no bias and no auto conversion. self.bias = False self.auto_convert = False def _read_u8(self, address): # Read an 8-bit unsigned value from the specified 8-bit address. with self._device as device: device.configure(baudrate=500000, phase=1, polarity=0) _BUFFER[0] = address & 0x7F device.write(self._BUFFER, end=1) device.readinto(self._BUFFER, end=1) return self._BUFFER[0] def _read_u16(self, address): # Read a 16-bit BE unsigned value from the specified 8-bit address. with self._device as device: device.configure(baudrate=500000, phase=1, polarity=0) self._BUFFER[0] = address & 0x7F device.write(self._BUFFER, end=1) device.readinto(self._BUFFER, end=2) return (self._BUFFER[0] << 8) | self._BUFFER[1] def _write_u8(self, address, val): # Write an 8-bit unsigned value to the specified 8-bit address. with self._device as device: device.configure(baudrate=500000, phase=1, polarity=0) self._BUFFER[0] = (address & 0xFF) | 0x80 self._BUFFER[1] = val & 0xFF self._device.write(self._BUFFER, end=2) @property def bias(self): """Get and set the boolean state of the sensor's bias (True/False).""" return bool(self._read_u8(_MAX31865_CONFIG_REG) & _MAX31865_CONFIG_BIAS) @bias.setter def bias(self, val): t = self._read_u8(_MAX31865_CONFIG_REG) if val: t |= _MAX31865_CONFIG_BIAS # Enable bias. else: t &= ~MAX31865_CONFIG_BIAS # Disable bias. self._write_u8(_MAX31865_CONFIG_REG, t) @property def auto_convert(self): """Get and set the boolean state of the sensor's automatic conversion mode (True/False). """ return bool(self._read_u8(_MAX31865_CONFIG_REG) & _MAX31865_CONFIG_MODEAUTO) @auto_convert.setter def auto_convert(self, val): t = self._read_u8(_MAX31865_CONFIG_REG) if val: t |= _MAX31865_CONFIG_MODEAUTO # Enable auto convert. else: t &= ~_MAX31865_CONFIG_MODEAUTO # Disable auto convert. self._write_u8(_MAX31865_CONFIG_REG, t) @property def fault(self): """Get the fault state of the sensor. Use the clear_faults function to clear the fault state. Returns a 6-tuple of boolean values which indicate if any faults are present: - HIGHTHRESH - LOWTHRESH - REFINLOW - REFINHIGH - RTDINLOW - OVUV """ faults = self._read_u8(_MAX31865_FAULTSTAT_REG) highthresh = bool(faults & _MAX31865_FAULT_HIGHTHRESH) lowthresh = bool(faults & _MAX31865_FAULT_LOWTHRESH) refinlow = bool(faults & _MAX31865_FAULT_REFINLOW) refinhigh = bool(faults & _MAX31865_FAULT_REFINHIGH) rtdinlow = bool(faults & _MAX31865_FAULT_RTDINLOW) ovuv = bool(faults & _MAX31865_FAULT_OVUV) return (highthresh, lowthresh, refinlow, refinhigh, rtdinlow, ovuv) def clear_faults(self): """Clear any fault state previously detected by the sensor.""" t = self._read_u8(_MAX31865_CONFIG_REG) t &= ~0x2C t |= _MAX31865_CONFIG_FAULTSTAT self._write_u8(_MAX31865_CONFIG_REG, t) def read_rtd(self): """Perform a raw reading of the thermocouple and return its 15-bit value. You'll need to manually convert this to temperature using the nominal value of the RTD and some math. If you just want temperature use the temperature property instead. """ self.clear_faults() self.bias = True time.sleep(0.01) t = self._read_u8(_MAX31865_CONFIG_REG) t |= _MAX31865_CONFIG_1SHOT self._write_u8(_MAX31865_CONFIG_REG, t) time.sleep(0.065) rtd = self._read_u16(_MAX31865_RTDMSB_REG) # Remove fault bit. rtd >>= 1 return rtd @property def temperature(self): """Read the temperature of the sensor and return its value in degrees Celsius. """ Rt = self.read_rtd() Rt //= 32768 Rt *= self.ref_resistor Z1 = -_RTD_A Z2 = _RTD_A * _RTD_A - (4 * _RTD_B); Z3 = (4 * _RTD_B) / self.rtd_nominal; Z4 = 2 * _RTD_B temp = Z2 + (Z3 * Rt); temp = (math.sqrt(temp) + Z1) / Z4 if temp >= 0: return temp rpoly = Rt temp = -242.02 temp += 2.2228 * rpoly rpoly *= Rt # square temp += 2.5859e-3 * rpoly rpoly *= Rt # ^3 temp -= 4.8260e-6 * rpoly rpoly *= Rt # ^4 temp -= 2.8183e-8 * rpoly rpoly *= Rt # ^5 temp += 1.5243e-10 * rpoly return temp